When your computer starts behaving strangely, won’t boot, or you start getting strange errors that you can’t pin down, a great way to troubleshoot the problem is to boot to a rescue disc and see if you can isolate the problem. It might be your operating system, it could be hardware, but you’ll never know until you boot to some other media to take a look. That said, there are tons of great system rescue discs to check out if you want a tool to save your ailing system. This week we’re looking at five of the best, nominated by you, our readers. [jump]

Earlier in the week, we asked you to nominate the best system rescue disc for our roundup. You rolled in with tons of great suggestions, and now we’re back to look at the top five.

The Trinity Rescue Kit is a customized Linux distribution that’s designed specifically for troubleshooting and reviving ailing systems, whether you’re running Windows or Linux. It fits nicely on a CD (or a USB stick if you prefer) and once booted gives you tools to reset lost Windows passwords, scan hard drives for viruses and malware, clone drives, recover lost partitions, even open up the drives as network shares so you can get files off of them and to other computers on your network. It’s completely free, although a donation to the developer behind it is always appreciated and keeps the project alive.

Hiren’s BootCD is pretty legendary, and anyone who’s ever worked in support or systems administration has probably used it at least once (or has several version of it lying around still.) The rescue disc is aimed squarely at repairing Windows systems, and includes a wealth of tools to that effect, including antivirus tools to scan your hard drive, anti-malware utilities to clean out spyware and adware, even rootkit detection tools. Hiren’s BootCD can also help you repair, adjust, or re-flash your system’s BIOS or wipe your CMOS, clean out temporary files and folders, securely erase files, back up your data to another hard drive or to the network, update and back up hardware drivers, scan your system for hardware failures, repair lost or damaged partitions, and much much more. We’re only scratching the surface here. It’s completely free and always has been. Even if there are other tools in your toolkit, Hiren’s BootCD should be among them.

The Ultimate Boot CD is another tool you’ll probably find in most technician’s disc binder. The Ultimate Boot CD is designed to troubleshoot Windows and Linux systems, and comes with a wealth of hardware testing, hard drive management, and partition troubleshooting and repair tools. The UBCD packs memory testing, CPU testing, and drive testing tools all onto the same disc, and even includes some BIOS management tools as well. If you’re having serious PC problems, the CD also includes a number of drive cloning and data recovery tools to help you get your files off of a problematic hard drive and somewhere safe. If you’re looking for a specifically Windows-targeted version of the Ultimate Boot CD, there’s always the Ultimate Boot CD for Windows, a rebuild of the disc that uses BartPE to create a pretty fully functional version of Windows XP once booted—and is also packed with many of the same troubleshooting tools. Both are free, but donations to the creators are always welcome.

Knoppix is a bootable Linux live CD that gives you a fully functional operating system once booted. You can use Knoppix to get familiar with linux (although it is highly customized) or just to boot to media other than your hard drive for troubleshooting, but in either case Knoppix is a whole OS—not just a customized interface to give you access to diagnostic and repair tools. It comes packed with a web browser (Firefox), Open Office, GIMP, and more, just in case you want to use it to get things done. Knoppix’s greatest benefit is its flexibility, and it can be customized to suit almost any need—you can download it and build your own installation with the troubleshooting tools you use most often, package it up, and then burn it to a CD or DVD yourself. If you’re a developer, the DVD version of Knoppix has even more extras for you. If you do need to use Knoppix for troubleshooting, there are data recovery and cloning tools built-in to make it easy. It’s free, and you can donate to the cause if you want, but since it’s completely open source, the developer notes that your time, code, and input is a more ideal way to contribute.

The aptly named System Rescue CD is a linux-based rescue disk designed to troubleshoot Linux and Windows systems and servers. The disk is packed with tools to help you manage or repair partitions, back up your data or clone your drives in case of a failure, and supports a wealth of file systems (even network file systems like NFS) so you can work with just about any file on any drive anywhere. The disc also comes with replacement bootloaders, system file editors, network troubleshooting and diagnostic tools, and disc burning tools so you can burn while you use the disc. There are also antivirus, anti-malware, and rootkit detection and removal tools. It’s completely free.

Now that you’ve seen the top five, it’s time to put them to an all-out vote to determine the winner.

Honorable mentions this week go out to Parted Magic, which a number of you nominated to handle those tricky MBR and partition problems in Windows and Linux, and to Puppy Linux, a great distro to get familiar with Linux, but that also has some great troubleshooting tools to resuscitate your computer if something goes terribly wrong.

The Hive Five is based on reader nominations. As with most Hive Five posts, if your favorite was left out, it’s not because we hate it—it’s because it didn’t get the nominations required in the call for contenders post to make the top five. We understand it’s a bit of a popularity contest, but if you have a favorite, we want to hear about it. Have a suggestion for the Hive Five? Send us an email at tips+hivefive@lifehacker.com!